Gastric Secretion

Question 1

What are the glands present in the stomach?

Answer 1

Gastric gland
Pyloric gland

Question 2

Location of the gastric gland

Answer 2

Proximal 80% of stomach (Fundus and body)

Question 3

Secretions of the gastric gland

Answer 3

Hydrochloric acid
Pepsinogen
Intrinsic factor
Mucus

Question 4

Location of the pyloric gland

Answer 4

Distal 20% of stomach (antrum and pylorus)

Question 5

Secretions of the pyloric gland

Answer 5

Mucus
Gastrin hormone (from G cells)
Somatostatin (from D cells)

Question 6

Functions of each cell of the gastric/oxyntic gland

Answer 6

Mucus neck cells secretesmucus and bicarbonate
Peptic (or chief) cells secretes pepsinogen
Parietal (or oxyntic)cells secreteshydrochloric acidandintrinsic factor.
Enterochromaffin-like(ECL)cellssecretes histamine

Question 7

Characteristics of gastric secretions

Answer 7

2500ml/day
Colorless
pH of 1 to 3.5 (acidic)
Composition: 99.5% water and 0.5% solids

Question 8

Types of solid components of gastric secretion

Answer 8

Inorganic: HCl, K+, Na+, Mg++ and HPO4
Organic: Mucus, enzymes (e.g, pepsinogen, lipase) and intrinsic factor

Question 9

What are the phases of gastric secretion?

Answer 9

Cephalic phase
Gastric phase
Intestinal phase

Question 10

Cephalic phase is caused by …

Answer 10

… sight, smell, thought and taste of food

Question 11

Cephalic phase account for how much gastric secretion

Answer 11

30%

Question 12

Origin of cephalic phase

Answer 12

Cerebral cortex and in the appetite centers of the amygdala and hypothalamus

Question 13

When does the gastric phase occur?

Answer 13

When food enters the stomach

Question 14

What occurs in the gastric phase?

Answer 14

Long vagovagal reflexes from the stomach to the brain and back to the stomach
Local enteric reflexes
Gastrin and histamine release

Question 15

Gastric phase accounts for how much of the gastric secretion?

Answer 15

60%

Question 16

When does the intestinal phase occur?

Answer 16

When food enters the duodenum

Question 17

Intestinal phase accounts for how much of gastric secretion?

Answer 17

10%

Question 18

Where is mucus secreted from?

Answer 18

Neck
Surface mucous cells
Gastric and pyloric glands

Question 19

Function of mucus

Answer 19

Forms mucus-bicarbonate barrier

Question 20

What can a distruption in the mucus-bicarbonate barrier cause?

Answer 20

Peptic ulcer

Question 21

Which cells secrete HCl?

Answer 21

Parietal cells

Question 22

What are the functions of hydrochloric acid?

Answer 22

PROBE ATTACK
Has a protective function against bacteria ingested with food
Breaks down and degrades food into smaller molecules
Activates pepsinogen into pepsin
Promote the absorption of calcium & iron

Question 23

Which cells secrete pepsinogen?

Answer 23

Cheif cells/Peptic cells

HCl activates pepsinogen into pepsin

Question 24

What are the functions of pepsin

Answer 24

Digestion of proteins

Question 25

Which cells secrete intrinsic factor?

Answer 25

Parietal cells

Question 26

What are the functions of intrinsic factor?

Answer 26

Absorption of Vitamin B12

Question 27

What does the absence of intrinsic factor cause?

Answer 27

Pernicious anemia

Question 28

Function of gastrin?

Answer 28

Stimulates gastric secretion and motility

Question 29

Function of somatostatin?

Answer 29

Inhibits gastric secretion and motility

Question 30

Describe the mechanism of HCL formation

Answer 30

Stage 1: H₂O and CO₂ use carbonic anhydrase enzyme to form H₂CO₃ (a week acid) which dissociates into H⁺ and HCO₃^-
Stage 2: H⁺ is secreted in exchange with K⁺ by H⁺-K⁺-ATPase proton pump at the luminal border
Stage 3: HCO₃ is reabsorbed to the blood stream in exchange with Cl^- at the basolateral border
Stage 4: Cl^- is secreted into the luminal border by CFTR channel

Question 31

What factors stimulate HCl production?

Answer 31

ACh (parasympathetic stimulation), gastrin and histamine

Question 32

What factors inhibit HCL secretion?

Answer 32

Somatostatin, prostaglandin, secretin and GIP

Question 33

How does parasympathetic stimulation affect HCl secretion?

Answer 33

Directly ACh acts on M3 receptor on the parietal cells and stimulate HCL secretion and inhibit somatostatin
Indirectly
Through stimulation of ECL cell to secrete histamine
Through stimulation of G cell to secret gastrin via release of gastrin releasing peptide (GRP)

Question 34

How does gastrin affect HCl secretion?

Answer 34

Stimulation by eating and by vagal stimulation
Increases H+through cholecystokinin B (CCKB) Gq-coupled receptors on parietal cells
Also a stimulator of histamine release from ECL cells

Question 35

How does histamine affect HCl secretion?

Answer 35

Binds H2receptors on parietal cells to increase H+through Gs-coupled receptors
Histamine release can be increased by ACh and gastrin, or it can be decreased by somatostatin

Question 36

How does somatostatin affect HCl secretion?

Answer 36

Directly inhibits parietal cells via Gireceptors in a paracrine and endocrine fashion. This means it affects both its neighboring cells as well as distant cells
Indirectly it is an important blocker of histamine and gastrin release

Question 37

How do prostaglandins affect HCl secretion?

Answer 37

Inhibitor of acid secretion at parietal cells and also act via Gireceptors

Question 38

What is a peptic ulcer?

Answer 38

It is due to breakdown of the barrier that protects stomach mucosa

Question 39

What are the causes of a peptic ulcer?

Answer 39

Infection with the bacterium Helicobacter pylori
Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs), which inhibit the production of prostaglandins
Zollinger-Ellison syndrome (gastrinoma)

Question 40

What are the treatments for a peptic ulcer?

Answer 40

H2 blocker (ranitidine)
Proton pump inhibitors (omeprazole)
prostaglandins analogues (misoprostol)